Certain metals can be plated on non-metallic surfaces by an autocatalytic plating process in which the surface is first treated with a sensitizing solution, then with an activating solution which precipitates nucleating sites. In this way, ceramics and many synthetic resins can be provided with coatings of nickel or copper, for example, which may or may not be later covered with a heavier layer of metal by electroplating.
The sensitizing solution most commonly used in the past contains Sn.sup..sup.+2 ions generally formed from the salt stannous chloride dissolved in hydrochloric acid. This material has proved to be quite satisfactory for electroless plating of metals on most non-metallic materials. However, there are certain materials, such as Teflon and silicone rubbers, as well as certain commercial photoresists, which cannot be satisfactorily plated by this method. The reason for the difficulty appears to be that these materials are unusually smooth and non-porous and are not readily wetted by aqueous solutions of stannous salts. As a result, when one attempts to deposit metal autocatalytically on one of these materials with no surface roughening, using conventional stannous salt sensitizers and conventional activators, such as palladium chloride, plating is spotty and otherwise non-uniform.
It should be noted that, in general, those who have used acidic solutions of stannous salts as electroless plating sensitizers, have tried to keep the tin ion in the divalent state by methods such as keeping metallic tin or other reducing agents, such as sugars, in the shelf stock solutions.
In addition to electroless plating, there are many other processes in which it is desired to convert hydrophobic surfaces to hydrophilic surfaces. For example, in painting with a water base paint, it may first be necessary to convert the surface to be painted from hydrophobic to hydrophilic. There is a need for simple and inexpensive ways to accomplish the conversion.